fix: tf-validate: remove TF_PROJECT_DIR from path

This commit fixes an issue in the tf-validate job where a path relative
to the root module path variable was used to remove the cached
.terraform/terraform.tfstate file.

This caused issues if the project directory was overridden because we
change the working directory to this path in .tf-base leading to an
incorrect location being tested.

This commit updates the tf-validate job to use a path relative to the
current directory instead, ensuring that the file is tested and removed
from the right location regardless of the project directory override.

Fixes: #89